1. Field of the Invention
The present invention relates to method and apparatus for manufacturing a lens having a lens body integral with a functional sheet, such as a polarizing sheet or an optical sheet for controlling the light transmission of the lens, on one side thereof by an insert molding process in which the functional sheet is inserted in a mold, and to a lens manufactured thereby.
2. Description of the Related Art
A method of manufacturing a lens is known which comprises an insert molding process including the steps of inserting into a mold a polarizing sheet previously formed into a curved surface, and then injecting a molten plastic material into the mold, thereby integrally molding a lens body and the polarizing sheet (refer to, for example, Japanese Examined Patent Publication No. SHO 61-56090). According to this conventional art, a flat peripheral portion around a curved surface portion of preformed polarizing sheet 51 is cut off with a portion retained as a support portion 52 as shown in FIG. 8; a support pin 57 is provided on a concave mold part 53 in an area outside a concave molding surface 54 thereof or on a convex mold part 55 in an area outside a convex molding surface thereof; the polarizing sheet 51 is gently placed on the concave molding surface 54 or the convex molding surface 56 conformably while the support portion 52 is supported by the support pin 57; and the mold parts 53 and 55 are clamped together and a molten plastic material is filled into a resulting cavity to form a lens having a lens body integral with the polarizing sheet 51.
It is said that, since the curved surface portion of the polarizing sheet 51 becomes in contact with the concave molding surface 54 of the concave mold part 53 (or the convex molding surface 56 of the convex mold part 55) with a slight play in the cavity though the support portion 52 of the polarizing sheet 51 is pinched between the mold parts 53 and 55, the molten plastic material entering the cavity is not substantially resisted by the polarizing sheet 51 and hence smoothly covers the polarizing sheet 51, resulting in a lens having a lens body free of any wrinkle and the polarizing sheet 51 with no crack.
With this method, however, at least an additional process of cutting off the support portion 52 by grinding is required even if the lens integrally having the polarizing sheet 51 can be used without being trimmed, thus resulting in the manufacture requiring additional time and labor. Further, since the polarizing sheet 51 between the mold parts 53 and 55 is anchored at the support portion 52 only, a peripheral portion of the polarizing sheet 51 is likely to be easily turned up by the inflow pressure of the plastic material or the like, so that the molten plastic material reaches the outward side of the polarizing sheet 51. This results in the polarizing sheet 51 or lens having deteriorated functions, hence, in a difficulty in manufacturing lenses of good quality.
In the insert molding process the art of anchoring the insert to a predetermined position by suction developed by a vacuum creating device is known. A lens manufacturing method based on the insert molding process utilizing such art is also known from, for example, Japanese Unexamined Patent Publication No. SHO 60-205401. According to this conventional method, mold parts 61 and 62, one of which defines a suction hole 63 opening at the center of the bottom thereof, are used as shown in FIG. 9; a previously formed first lens 64 is placed in position between the mold parts 61 and 62; a vacuum pump is actuated to attract the first lens 64 against the mold part 61 through the suction hole 63 to anchor the first lens 64 onto the mold part 61; and the other mold part 62 is mated with the mold part 61, followed by injection of a molten plastic material into the resulting cavity to afford an intended hybrid lens.
This conventional art does not require the grinding process which is required after the insert molding in the former conventional art shown in FIG. 8. However, since a central portion of the first lens 64 is attracted by a large suction force though the suction hole 63 defined centrally of the mold part 61 and connected to the vacuum pump, a relatively large suction mark will result in a central portion of a functional sheet such as a polarizing sheet, if the functional sheet is used as an insert instead of the first lens 64. This significantly deteriorates the functions of the functional sheet or lens to the extent that it is difficult to make correction after the insert molding. Additionally, the provision of the suction hole 63 in the central portion of the mold part 61 may cause a similar problem as in the former conventional art shown in FIG. 8; that is, a peripheral portion of the polarizing sheet 51 is likely to be easily turned up by the inflow pressure of the plastic material or the like, so that the molten plastic material reaches the outward side of the polarizing sheet 51, thus resulting in the polarizing sheet 51 or lens having deteriorated functions.
In view of the foregoing problems involved in the prior art, it is an object of the present invention to provide lens manufacturing method and apparatus which can securely hold an insert such as a functional sheet on a molding surface of a mold in an insert molding process without any danger of turning up a peripheral portion of the functional sheet and can easily manufacture a lens of good quality without any substantial deterioration in the functions of the functional sheet or lens.